Rethinking LANDfill Diversion: Why Liquid Waste Like Grease Traps Can Mislead the Metrics

Steve Luxford
Apr 9
3 min read

In the pursuit of greener operations, many facilities and municipalities tout impressive landfill diversion percentages. But what if those numbers aren’t telling the full story?

🚗 Volkswagen’s “Clean Diesel” Scandal: Remember when Volkswagen marketed its diesel cars as “eco-friendly”—only for the world to find out they had installed software to cheat emissions tests? On paper, their cars looked green, but in reality, they were emitting up to 40 times the legal pollution limits.

The same kind of statistical trickery happens in landfill diversion reporting. Some companies include liquid waste, like grease traps, in their numbers—waste that was never destined for landfill in the first place. It looks like a big win, but in reality, it doesn’t reflect actual landfill reduction.

Here’s why we need a more nuanced approach.

Waste Vendors & Inflated Diversion Claims

Waste contractors know that high diversion rates make their offers more attractive in tenders. Some artificially boost their numbers by including waste streams—like grease traps and waste oil—that were never meant for landfill.

To assess landfill diversion rates accurately, it’s essential to understand the key terms:

Solid waste – Materials such as general waste, recyclables, organics, and other physical items disposed of by businesses and households. These materials are typically sent to landfill, recycling facilities, or composting operations.
Liquid waste – Includes wastewater, grease trap waste, used oils, and other fluid by-products from industrial and commercial operations. Unlike solid waste, it is processed through treatment plants, converted into by-products, or repurposed through specialised disposal methods.
Landfill diversion – A metric measuring the percentage of waste prevented from going to landfill through recycling, composting, or other forms of recovery.

While diversion is a valuable sustainability indicator, including liquid waste artificially inflates the numbers, as it was never going to landfill in the first place.

📌 Your Responsibility: If a vendor promises a 90%+ diversion rate, dig into the details. Ensure the data is:

✅ Fair – Does it reflect actual landfill diversion?

✅ Transparent – Are liquid and solid waste streams reported separately?

✅ Aligned with industry standards – Is it comparable to real landfill reduction metrics? Does it align with your intended goals?

Illustration showing how grease trap waste is misclassified as diverted from landfill, highlighting misleading waste diversion reporting practices. — Grease Trap Waste Is Not Accepted at Landfill – So Why Include It in Diversion Metrics?

Why Liquid Waste Should Be Reported Separately

Unlike solid waste, which can be recycled or composted, liquid waste follows a different treatment path—it is processed in wastewater facilities, converted into biodiesel, or handled through other methods. Lumping it into diversion metrics misrepresents actual landfill reduction.

For example, if a company claims 90% waste diversion but includes liquid waste, the true solid waste diversion rate could be much lower. This distorts sustainability claims and undermines meaningful progress in landfill reduction.

Infographic outlining landfill diversion targets and how misreporting—such as including liquid waste—can distort true waste reduction outcomes. — Impact of Including Liquid Waste in Landfill Diversion Rates

The Risks of Inflated Metrics

📉 False Progress – Including liquid waste inflates diversion rates, making organisations believe they are reducing landfill when solid waste disposal remains unchanged.

🚫 Regulatory Risks – Misleading data can lead to poor policy decisions, misplaced investments, and ineffective waste reduction strategies.

🔍 Missed Opportunities – Inflated numbers distract from real solutions like better recycling, contamination reduction, and waste minimisation.

Moving Towards More Accurate Metrics

Streamlined Reporting

A more accurate sustainability assessment requires separating waste streams. Reporting liquid waste from grease traps separately from traditional solid waste provides clearer insights. This transparency allows organisations to:

✔ Improve recycling programs for solid waste

✔ Optimise treatment processes for liquid outputs

✔ Ensure accurate reporting in tenders and sustainability goals

Beyond Landfill Diversion Metrics

Waste management should go beyond simple diversion percentages. More meaningful metrics include:

✅ Kg per person – Tracks waste generated per capita over time.

✅ Kg per area (m² or building) – Helps compare waste generation across sites.

✅ Contamination rates – Measures incorrect waste sorting to improve recycling.

✅ Carbon footprint of waste – Tracks emissions from disposal methods.

Using these benchmarks ensures accurate tracking and real progress, rather than inflated diversion figures.

Deep Below the Diversion: Where the Real Impact Lies

While it might be tempting to include all waste in landfill diversion statistics, doing so—especially with liquid waste like grease traps—inflates environmental performance figures.

A more precise approach focuses on actual landfill reduction, differentiating waste types and ensuring transparency in sustainability reporting. By refining these metrics, we can truly measure progress and direct efforts where they matter most—towards real landfill reduction.